Blood collection and processing play important roles in the worldwide health care system. In conventional blood collection, blood is removed from a donor or patient, separated into its various blood components via centrifugation, filtration and/or elutriation and stored in sterile containers for future infusion into a patient for therapeutic use. The separated blood components typically include fractions corresponding to red blood cells, white blood cells, platelets and plasma. Separation of blood into its components can be performed continuously during collection or can be performed subsequent to collection in batches, particularly with respect to the processing of whole blood samples. Separation of blood into its various components under highly sterile conditions is critical to most therapeutic applications.
Recently, apheresis blood collection techniques have been adopted in many blood collection centers wherein a selected component of blood is collected and the balance of the blood is returned to the donor during collection. In apheresis, blood is removed from a donor and immediately separated into its components by on-line blood processing methods. Typically, on-line blood processing is provided by density centrifugation, filtration and/or diffusion-based separation techniques. One or more of the separated blood components are collected and stored in sterile containers, while the remaining blood components are directly re-circulated to the donor. An advantage of this method is that it allows more frequent donation from an individual donor because only a selected blood component is collected and purified. For example, a donor undergoing plateletpheresis, whereby platelets are collected and the non-platelet blood components are returned to the donor, may donate blood as often as once every fourteen days.
Apheresis blood processing also plays an important role in a large number of therapeutic procedures. In these methods, blood is withdrawn from a patient undergoing therapy, separated, and a selected fraction is collected while the remainder is returned to the patient. For example, a patient may undergo leukapheresis prior to radiation therapy, whereby the white blood cell component of his blood is separated, collected and stored to avoid exposure to radiation. Alternatively, apheresis techniques may be used to perform red blood cell exchange for patients with hematological disorders such as sickle cell anemia and thalassemia, whereby a patient's red blood cell component is removed and donated packed red blood cells are provided to the patient along with his remaining blood components. Further, apheresis may be used to perform therapeutic platelet depletion for patients having thrombocytosis and therapeutic plasma exchange for patients with autoimmune diseases.
Both conventional blood collection and apheresis systems typically employ differential centrifugation methods for separating blood into its various blood components. In differential centrifugation, blood is circulated through a sterile separation chamber, which is rotated at high rotational speeds about a central rotation axis. Rotation of the separation chamber creates a centrifugal force directed along rotating axes of separation oriented perpendicular to the central rotation axis of the centrifuge. The centrifugal force generated upon rotation separates particles suspended in the blood sample into discrete fractions having different densities. Specifically, a blood sample separates into discrete phases corresponding to a higher density fraction comprising red blood cells and a lower density fraction comprising plasma. In addition, an intermediate density fraction comprising platelets and leukocytes forms an interface layer between the red blood cells and the plasma. Descriptions of blood centrifugation devices are provided in U.S. Pat. No. 5,653,887 and U.S. patent application Ser. No. 10/413,890.
To achieve continuous, high throughput blood separation, extraction or collection ports are provided in most separation chambers. Extraction ports are capable of withdrawing material from the separation chamber at adjustable flow rates and, typically, are disposed at selected positions along the separation axis corresponding to discrete blood components. To ensure the extracted fluid exiting a selected extraction port is substantially limited to a single phase, however, the phase boundaries between the separated blood components must be positioned along the separation axis such that an extraction port contacts a single phase. For example, if the fraction containing white blood cells resides too close to the extraction port corresponding to platelet enriched plasma, white blood cells may enter the platelet enriched plasma stream exiting the separation chamber, thereby degrading the extent of separation achieved during blood processing. Although conventional blood processing via density centrifugation is capable of efficient separation of individual blood components, the purities of individual components obtained using this method is often not optimal for use in many therapeutic applications. For example, centrifugation separation of blood samples is unable to consistently (99% of the time) produce separated platelet components which have less than 1×106 white blood cells per every 3×1011 platelets collected. The presence of white blood cells in platelet products increases the risks of viral exposure and immunological complications upon infusion into a patient.
The purity of extracted blood components using density centrifugation is currently limited by the control of the position of phase boundary layers between separated components provided by conventional centrifugation devices and methods. The position of phase boundaries along the separation axis depends on a number of variables. First, phase boundary positions depend on the relative flow rates of individual blood components out of the separation chamber. Second, phase boundary positions depend on the rotational velocity of the separation chamber about the central rotation axis and the temperature of the blood undergoing separation. Third, phase boundary positions vary with the composition of the blood undergoing processing. Blood sample composition may vary considerably from donor to donor and/or from patient to patient. In addition, blood composition may vary significantly as function of time for a given donor or patient, especially as blood is recycled through the separation chamber multiple times. Given the sensitivity of the phase boundary position to many variables, which change from person to person and during processing, it is important to monitor the position of the phase boundaries during blood processing to ensure optimal separation conditions are maintained and the desired purity of selected blood components is achieved. In addition, accurate characterization of the positions of phase boundaries allows for separation conditions to be adjusted and optimized for changes in blood composition during processing.
It will be appreciated from the foregoing that a need exists for methods and devices for monitoring and controlling the processing of whole blood samples and blood component samples. Particularly, optical monitoring methods and devices are needed which are capable of accurately characterizing the separation, extraction and collection of blood components processed by density centrifugation, including providing controlled stroboscopic light sources with consistent duration and intensity of illumination. An effective light source and a control mechanism are disclosed in U.S. application Ser. No. 10/905,353 and its divisional application Ser. No. 11/867,816. These applications provide stroboscopic LED light sources for use with devices for improving the processing of fluids, such as blood, components of blood and fluids derived from blood. The application relates to apparatus for controlling the processing of blood into blood components, particularly components for stroboscopic LED light sources for centrifuges. The stroboscopic apparatus comprises a first light source with reflective surfaces spaced around a central illumination axis, and light-emitting diodes spaced away from the axis radially outward from the reflective surfaces. An additional light source comprises a modified parabolic reflector surrounding a light emitting diode, the parabolic reflector having walls spaced outwardly from an axis of symmetry such that focal points fall radially outwardly from a center of the LED, forming a circular focal area. A controller that energizes the diodes for selected periods of time comprises a pair of switches connected in series, with an LED connected between the switches. One of the switches is connected to ground and is closed at the end of a period of illumination.
An exemplary optical monitoring system for a density centrifuge having a separation chamber rotating about a central rotation axis comprises at least one light source, a light collection element and a detector. Rotation of the separation chamber about a central rotation axis results in separation of the blood components in the separation chamber according to density along rotating separation axes oriented perpendicular to the central rotation axis of the centrifuge. Both the light source and light collection element are arranged such that they are periodically in optical communication with an observation region positioned on the density centrifuge. In one embodiment, the light source and detector are arranged such that an optical cell of the separation chamber is periodically rotated into and out of the observation region. The light sources are capable of generating an incident light beam having a selected wavelength range including, but not limited to, visible light, infrared light and/or ultraviolet light. It has been found, however, that diffusing a focused, columnar light beam near the observation region can improve performance.